The invention generally relates to a formation isolation valve.
A formation isolation valve may be used in a well for such purposes as preventing fluid loss and controlling an underbalanced condition. The valve forms a controllable sealed access to formations below the valve. When the valve is open, well equipment (a tubular string, a wireline system, a slickline system, etc.) may be deployed through the valve for purposes of performing one or more testing, perforating and/or completion functions below the valve. After these functions are complete, the well equipment may be retrieved, and the valve may be subsequently closed.
For purposes of opening and closing the valve, a tool, such as a shifting tool that is disposed at the end of a string, may be used to physically engage the valve. More specifically, the shifting tool interacts with a mechanical section of the valve. The mechanical section typically is tied to a barrier valve element (a ball valve element, for example) of the valve so that linear motion of the shifting tool (caused by controlled movement of a string connected to the shifting tool, for example) acts to either directly or indirectly open or close the valve element. In addition, the mechanical section holds the valve element in position (i.e., keeps the valve either open or closed) after the shifting tool is removed from the valve.
As a more specific example, the mechanical section of a typical formation isolation valve may include at least one collet that is constructed to engage a detent for purposes of locking the valve in either an open or closed position. When a sufficient force is applied to the mechanical section by the shifting tool to overcome a shifting force threshold, the collet is released from the detent to unlock the valve. The movement of the collet may scrape the interior of the valve and may wear down the holding edge or face of the collet, thereby decreasing the holding capability of the collet. Additionally, the shifting force threshold that must be overcome to release the collet from the detent relies largely on the flexibility of the collet and the angular relationship between the holding edge or face of the collet head and the detent. As a result, the shifting force threshold may be inconsistent and somewhat unreliable from unit to unit.
The mechanical section should have a relatively high holding force and a relatively low shifting force threshold. The holding force and the shifting force threshold, however, are established by the same geometry of the collet and the detent. Therefore, challenges exist in designing a formation isolation valve that satisfactorily satisfies both criteria.